Identification and analysis of offset printing ghosts

Ghosting refers to the appearance of silhouette or phantom images around the printed artwork. It can be divided into axial ghosting and circumferential ghosting according to different directions. The axial ghost is at a smaller angle to the axis of the drum, and the circumferential ghost is perpendicular to the axis of the drum. The following describes the causes of several ghosting failures.

1. The blanket is not stretched tightly, resulting in full or partial circumferential ghosting. There are two situations.

(1) The overall blanket is not stretched so tightly that the blanket cannot be reset in time after compression, resulting in overall ghosting.

(2) The blanket is cut or installed in a skewed position, resulting in localized ghosting and partial ghosting. At this point, stretch the blanket or reinstall the blanket to solve the problem.

2. The roller pressure is too large, causing overall circumferential ghosting. The roller pressure should be adjusted according to the thickness of the printed paper.

3. The overprinted paper quit, resulting in a dozen sheets of paper in the upper layer. The direction of this ghosting is not fixed and will be more and more light.

4. The paper is uneven and the water content is uneven, causing partial ghosting. The position is not fixed. Sometimes it is not. When it is light, it is heavy.

5. The plate is not tightened or cracked at both ends of the plate, resulting in a full or partial circumferential ghosting.

6. Two-color machine impression cylinder The gripper pad is lower than the roller surface, and the impression cylinder rubs against the paper, and the paper cannot be tightly attached to the roller after a period of time after the embossing roller is smashed. After the stamping of the first color blanket, most of the arches disappeared. When the second color blanket was imprinted, there was still a small amount of arching. Due to the slight difference in arching, it was sometimes impossible to work on the first color blanket. Dot blots completely overlap, causing ghosting.

7. Impression cylinder gripping force is too small, uneven, grippers and tooth pads serious wear, too smooth, or a lot of ink volume, viscosity, make the paper move in the gripper. Due to the difference in the amount of movement, the dots of the two blankets cannot overlap, and ghosts appear.

8. The roller gear and bearing wear, the clearance becomes larger, when the machine is suddenly loaded, the roller generates ghost due to vibration. In addition, if the roller bearings are loose and the thrust bearing is not locked, it will cause ghosting.

There are many causes of ghosting. When you encounter ghosting problems, you should first analyze the type of ghosting, find the cause according to its type, and troubleshoot.